The present invention relates generally to an apparatus for data transfer with a rotating data storage disk, particularly an optical disk, and more particularly a recordable compact disk (CD-R), or an optical disk of the known write-once variety, on which data can be written once and read many times. Still more particularly, the invention pertains to improvements in an automatic laser power control (ALPC) conventionally included in an optical disk drive for holding constant the intensity of the light beam scanning the disk, specifically dealing with how to optimize the target value at which the beam intensity is to be held during reading, rather than writing, against the unavoidable offset of the control system.
An unused CD-R, commercially available today, has a preformed groove, or pregroove, cut in its surface in the form of a multiturn spiral, along which the light beam is to be guided for writing. Irradiating the pregroove, the light beam provides a tracking error signal which is used for tracking control, that is, for keeping the beam spot centered on the track. The pregroove slightly xe2x80x9cwobblesxe2x80x9d in a regular zigzag fashion, such that when the beam scans it at a prescribed linear velocity for writing, the tracking error signal includes a wobble component with a standard frequency of 22.05 kHz.
The tracking error signal with the wobble component serves some important purposes in addition to tracking control. One of them is disk speed control. The disk speed is servo controlled so as to maintain the wobble signal at 22.05 kHz. Another purpose is the provision of the positional information of the beam spot on the disk. The wobble frequency on the disk is frequency modulated at 22.05 kHzxc2x11 kHz to include track address information known as ATIP (absolute time in pregroove). This address information is therefore derivable from the wobble component of the tracking error signal.
Recording on CD-Rs is done under the control of write pulses. User data is written during the durations of the write pulses, and the wobbling pregroove is read during the pulse spacings to provide the tracking error signal with the wobble component. Writing is alternate, or almost concurrent, with reading. The light beam tracing the pregroove is alternately switched between write intensity and read intensity with the progress of alternate writing and reading.
It has been known and practiced widely to incorporate an ALPC in optical disk drives in order to keep constant the intensities of the light beam scanning the disk. The ALPC is known to reduce fluctuations in the light beam intensities due to changes in ambient temperature, deterioration of the parts with the lapse of time, and other causes, contributing to more reliable performance of the related servos and signal processing systems.
The prior art ALPC (shown in FIG. 1 of the drawings attached hereto) has had a problem left unsolved in connection with the offset unavoidably arising in the control system for various reasons, among them being the over- and undershooting of the output waveform of the photodetector monitoring the light beam intensity. In the absence of any countermeasures the offset could make the ALPC incapable of holding the light beam at a desired write intensity and a desired read intensity. As regards the write beam intensity, it has been suggested to determine, immediately before recording, an optimum target value at which the write beam is to be held in the succeeding recording session. The effects of the system offset has proved to be virtually eliminated through optimization of the write target value in consideration of the offset existing at that time.
Concerning the read beam intensity, however, no such preliminary optimization against offset has so far been practiced. Pregroove reading during writing is no negligible matter, being intended as aforesaid for the important functions of tracking control, track address detection, and so forth. Accurate execution of these functions has in some cases been seriously hampered by undesired deviations of the read beam intensity from the target value due to offset.
The present invention has it as an object, in an data transfer apparatus for use with a rotating optical disk, to make the intensity of the light beam unaffected by system offsets due to various possible causes noted above.
Another object of the invention is to optimize the intensity of the light beam reading the wobbling pregroove in an optical disk for accurate tracking control, disk speed control, track address detection, and other purposes.
Another object of the invention is to make it possible for the user to readily update the read beam intensity target.
A further object of the invention is to make it possible for the user to determine an optimum read beam intensity target for the particular write beam intensity target to be used subsequently in recording.
Briefly, the present invention may be summarized, in an apparatus utilizing a beam of light for optically writing and reading information on a rotating disk, a light beam intensity control system comprising a driver circuit connected to a light source for causing the same to emit a light beam of consistently read intensity or, in response to write pulses, of alternating write intensity and read intensity. A write intensity control circuit is provided for finding a difference between an actual write intensity signal, indicative of the actual write intensity of the light beam, and a write intensity target signal indicative of a target value at which the write intensity of the light beam is to be held. The write intensity control circuit is connected to the driver circuit for causing the same to control the write intensity of the light beam according to the difference found. Also connected to the driver circuit is a read intensity control circuit for applying thereto a read intensity control signal thereby to cause the driver circuit to control the read intensity of the light beam according to a difference between an actual read intensity signal and a read intensity target signal.
The invention particularly deals with the improved construction of a read intensity target generator for generating the noted read intensity target signal indicative of a target value at which the read intensity of the light beam is to be held. The improved read intensity target generator comprises means connected to the read intensity control circuit for detecting an offset component of the read intensity control signal, and means for amending the read intensity target signal so as to cancel the detected offset component of the read intensity control signal.
An offset will occur for various reasons other than the over- and undershooting of the monitoring waveform of the light beam intensity. Therefore, according to more specific aspects of the invention, the offset is first detected while the light beam is held in consistently read intensity. Then, after compensating for the offset thus detected, offset detection is again made by switching the light beam between read and write intensities at the same rate as in recording on the disk, and the read intensity target is amended and optimized accordingly.
With the read beam target optimized in this manner, the read beam will be stably maintained at that target intensity as it reads the wobbling pregroove in subsequent recording on the disk. Accurately reading the information, the stable intensity read beam will enable proper execution of the functions for which it is intended. Moreover, since the read beam intensity control system according to the invention tolerates some over- and undershooting of the monitoring waveform, no expensive wave form amplifier and the like are required.
According to another important feature of the invention, in detecting the offset while the light beam is being switched between read and write intensities as above, the read intensity target is amended at two different notional write intensity targets above and below, respectively, the actual intended write intensity target to be used in subsequent recording. The optimum read intensity target for the actual write intensity target is computed subsequently by a prescribed expression using the amendments made on the normal read target at the two notional write intensity targets.
The overshooting of the monitoring waveform is proportional to the write intensity. The read intensity target may be optimized in this manner for any write intensity target intended for use. Carried out in a minimal period of time prior to recording, the read intensity target optimization according to the invention is not to interfere with actual recording in any way.
The above and other objects, features and advantages of this invention and the manner of achieving them will become more apparent, and the invention itself will best be understood, from a study of the following description and attached claims, with reference had to the accompanying drawings showing the preferred embodiments of the invention.